Liquid crystal display devices are being used in watches, calculators, various measurement instruments, automobile panels, word processors, electronic organizers, printers, computers, televisions, clocks, advertising boards, etc. Typical examples of the liquid crystal display mode include TN (twisted nematic) mode, STN (super twisted nematic) mode, and VA (hereinafter may be referred to as vertical alignment) mode and IPS (in-plane switching) mode that use TFTs (thin film transistors). Liquid crystal compositions that are used in these liquid crystal display devices are required to be stable against external factors such as moisture, air, heat, and light, stay in a liquid crystal phase in a temperature range as wide as possible about room temperature, exhibit low viscosity, and operate at a low drive voltage. A liquid crystal composition is constituted by several to dozens of compounds in order to optimize dielectric anisotropy (Δ∈), refractive index anisotropy (Δn), and other physical properties for individual display devices.
For example, in VA-mode displays widely used in liquid crystal televisions and the like, liquid crystal compositions having a negative Δ∈ are typically used. In TN-mode displays used in PC monitors and the like and IPS-mode displays widely used in touch panels and the like, liquid crystal compositions mainly having a positive Δ∈ are typically used. Naturally, in displays of all drive modes including these IPS and VA modes, a liquid crystal composition that enables a low-voltage drive, high-speed response, and a wide operation temperature range is sought after. In order to meet these needs, a liquid crystal composition that has Δ∈ with a high absolute value, a low viscosity (η), and a high nematic phase-isotropic liquid phase transition temperature (Tni) is required.
Moreover, because of the setting of Δn×d, which is the product of Δn and a cell gap (d), the Δn of the liquid crystal composition needs to be adjusted to be within a range appropriate for the cell gap. In addition, when a liquid crystal display device is applied to a television or the like, high response speed is important and thus a liquid crystal composition with a low γ1 is required. Currently, high response speed is achieved by adding a dielectrically neutral compound with a relatively low molecular weight to a liquid crystal composition so as to decrease the viscosity of the entire liquid crystal composition.
However, PTL 1 discloses that a dielectrically neutral compound added to ensure high speed response is a cause of an image ghosting phenomenon (also called burn-in phenomenon and covers linear afterimages and planar afterimages) in televisions (refer to paragraphs 0020 and 0021 in PTL 1). In other words, according to PTL 1, because a problem of image fixing occurs due to an interaction between an alignment layer and a liquid crystal composition containing a neutral alkenyl compound, a bicyclohexyl-(benzene) skeleton (refer to formula (I) in PTL 1) having alkyl groups at two ends is used as an essential component of the liquid crystal composition to eliminate or significantly reduce image fixing after long hours of operation, thereby resolving this problem.
Another technologies of suppressing or preventing ghosting in a system that contains a dielectrically neutral compound is disclosed in PTL 2. PTL 2 discloses a composition that contains, as essential components, a neutral compound that does not show dielectric anisotropy and a fluorine-containing compound (refer to general formula (I) in PTL 2) having a skeleton in which a benzopyran ring and a cyclohexane ring are bonded to each other via an ether bond. According to PTL 2, the content of the fluorine-containing compound having one cyclohexyl ring is limited or the content of a neutral compound having alkenyl groups as terminal groups is limited so as to reduce the reaction between a liquid crystal composition and ion impurities.